1. Field of the Invention
The purpose of the present invention is to provide an improved atherectomy system where treatment of undesirable deposits in the vasculature ranging from soft clots to harder plaque is provided. The major problems faced by current atherectomy devices include vessel safety, embolization, and ease of use. Potentially, all of those issues are addressed by the design of and are incorporated into the operation of the present invention. Coagulated blood, fatty deposits, plaque, grumous or other built-up material generally referred to as thrombus is developed in-vivo in the body. As time goes on, this coagulated blood becomes more organized and tough. Thrombus that resides in the vessels even a few days can limit the impact of thrombectomy catheters, such as an AngioJet®, for complete removal. Thus, one potential application of the present invention is to remove organized clots that are resistant to traditional thrombectomy catheter treatment. Alternatively, arterial disease is a progression of atheromatous material, a soft fatty buildup within a blood vessel. The disease process is dependent upon a variety of factors including diet, exercise, patient genetic profile, diabetes, etc. The formation of atheromas in the heart is typically treated by coronary stenting procedures (Percutaneous Coronary Intervention (“PCI”)). In the case of PCI, the stenotic portion of the vessel (a constricted section of the vessel due to thickening of the vessel wall with plaque deposits) is opened with a balloon and supported with a stent. In some cases, it may be desirable to remove a portion of the plaque rather than using a stent. For example, lesions in the vicinity of the ostium of a coronary artery may result in plaque shifting when stented, resulting in blockage of a different coronary artery. In those cases, it may be preferred to remove plaque, even if stenting is intended. In the case of peripheral arterial disease, there has not been a good track record of maintaining patent vessels in the leg arteries by using stents. Some of the difficulties with stenting the leg arteries are the severe flexing of the arteries. As one bends a knee, the arteries are bent as well. Structural supports, such as stents, are difficult to devise such that they provide the desired structural support and necessary flexibility. Recently there has been some interest in using atherectomy as an alternative to stenting of arterial lesions in the leg. The SilverHawk® device by Fox Hollow Technologies, Inc. of Delaware is an atherectomy device that is used primarily in the legs for arterial debulking. The present invention is similar to the Fox Hollow device in that both remove atheromatous material. However, the present invention offers a novel way of evacuating the debris as it is being removed that is not possible with the currently marketed Fox Hollow device.
2. Description of the Prior Art
Three notable marketed atherectomy devices include the Rotablator® (Boston Scientific Corporation), the SilverHawk® (Fox Hollow Technologies, Inc.), and the Simpson AtheroCath® Catheter (formerly with Guidant). In the case of the Rotablator®, a spinning burr is used to cut through tough material. The burr is designed to avoid damaging a healthy vessel and yet enable cutting of the plaque. Allegedly, the Rotablator® produces embolic debris while ablating the stenotic lesion. The tip of the Rotablator® becomes hot from the work performed so it is under a constant purge of saline. Thus, embolic debris is flushed into the vascular bed. Contrary to the statement above, there is some concern about the production of this embolic debris. Secondly, the Rotablator® system has been characterized as time intensive to set up. There are various connections required. Thus, ease of use is also a concern. The rotational aspect to the device means it is not a directional atherectomy device. Thus, if the plaque is positioned on one-half of the vessel, the device would still contact the healthy side of the vessel as it performed its atherectomy function.
The second device mentioned has made a large impact in the treatment of peripheral arterial disease. Since stenting has not proven ideally efficacious in the long term patency of the treated vessels, atherectomy has become popular. The SilverHawk® device uses a rotational cutter to skive away the plaque. It is a directional atherectomy device. Similar to the present invention, it has a bent tip to position the cutter against the atheroma. The device is reported to be acceptably easy to set up. The issues with the device involve vessel safety and embolization. Physician discussions of complications with peripheral interventions have involved the use of the SilverHawk® device followed by an observed perforation of the artery. Secondly, the device directs the skived material (it whittles out strips of the plaque versus sanding it away) toward the tip of the catheter. Once the tip is full of these skived strips, there have been reported instances of excess debris being sent distally (embolization). Therefore, the physician must constantly remove the device from the patient to unload the tip.
The AtheroCath® is similar to the Possis Medical, Inc. atherectomy device in U.S. Pat. No. 5,496,267. In the case of the AtheroCath®, a balloon directs an opening in the catheter against the lesion. A metal cutter is advanced and any material caught inside the opening is excised (like a biopsy). In the case of U.S. Pat. No. 5,496,267, the balloon directs the opening in an AngioJet® style atherectomy catheter against a lesion. Any material that is caught inside the opening is presumably macerated by the high velocity fluid jets. It is evident that the AngioJet® style device in U.S. Pat. No. 5,496,267 would at least afford a means of conducting atherectomy in a continuous process. The Simpson catheter would be difficult to operate in long stretches of diseased vessel. Furthermore, both devices suffer from not encouraging material to be removed. For example, imagine that the devices are 2 mm in diameter and that the stenosis is a hard circumferential stenosis with smooth surface and an ID of 3 mm. The balloon would push the devices against the hard material, but none would enter the cutting region since it is a hard smooth surface. Hence, no material would be removed.
Possis Medical, Inc. currently manufactures the AngioJet® system which is used in coronary arterial, peripheral arterial, and arterial venous access graft interventional procedures for the removal of thrombus. The AngioJet® system uses high velocity fluid jets to generate secondary flow patterns at the catheter tip for the dislodgement, maceration, and removal of thrombus. The AngioJet® system originated as an idea for removal of atheromatous material by directing high velocity fluid jets at the hard diseased tissue. However, the high velocity fluid jets will not distinguish between diseased tissue and the healthy vessel wall. Therefore, the catheter design evolved to direct the high velocity fluid jets internally inside the catheter. This design proved to be able to remove thrombus while leaving the vessel wall unharmed. Nevertheless, it was recognized years ago that these high velocity fluid jets could prove useful in removing atheromatous material as well. Possis Medical, Inc. patented an atherectomy device using these high velocity fluid jets, U.S. Pat. No. 5,496,267.